Distribution cable with permanently connected branch cables and method of effecting said connections

ABSTRACT

An electrical distribution cable comprises a neutral conductor and a number of insulated power conductors all helically laid up together and having branch cables permanently connected to it at spaced locations along its length before it is installed. Each of the branch cables comprises at least one insulated power conductor which is connected to a power conductor of the distribution cable and a neutral conductor, in the form of an outer concentric conductor which is connected to the neutral conductor of the distribution cable by a metal strip wrapped around the outer concentric conductor of the branch cable and the assembly of cores of the distribution cable and permanently secured to the outer concentric conductor of the branch cable and to the neutral conductor of the distribution cable.

[ Mar. 5, 1974 United States Patent [191 Higgins 837,352 6/1960 Great156/49 DISTRIBUTION CABLE WITH PERMANENTLY CONNECTED BRANCH PrimaryExaminer--Laramie E. Askin &

or Firm-Buell, Blenko Attorney, Agent,

Ziesenheim Peter Higgins, Hounslow, England [73] Assignee: BritishInsulated Gallenders Cables [57] ABSTRACT An electrical distributioncable comprises a neutral Limited, London, England Oct. 2, 1972conductor and a number of insulated power conductors all helically laidup together and having branch [22] Filed:

[21] Appl. No.: 294,077 cables permanently connected to it at spacedlocations along its length before it is installed. Each of the branchcables comprises at least one insulated power conductor which isconnected to a power vconductor 0 C0 m4 7 0 H m2 Wm 23 h 0 H a 4" 7 C Snum 11 21 55 [1 of the distribution cable and a neutral conductor, in

the form of an outer concentric conductor which isconnected to theneutral conductor of the distribution cable by a metal strip wrappedaround the outer con- [56] References Clted centric conductor of thebranch cable and the assem- UNITED STATES PATENTS bly of cores of thedistribution cable and permanently 12/1971 FOREIGN PATENTS ORAPPLICATIONS 3,626,082 Kasai et al. 174/72 R secured to the outerconcentric conductor of the branch cable and to the neutral conductor ofthe distribution cable.

647,512 8/1962 Canada............................. 174/71 R 727,1113/1955 Great Britain 174/71 R 11 Claims, 1 Drawing Figure PATENTEW3,795.75?

1m comma DISTRIBUTION CABLE WITH PERMANENTLY CONNECTED BRANCH CABLES ANDMETHOD OF EFFECTING SAID CONNECTIONS This invention relates to electricpower distribution cables comprising a neutral conductor and a number of5 insulated power conductors (or cores), normally one for each phase,all helically laid up together. Such cables are used for localdistribution of power to consumers, for example in houses or factories,through'single or multi-phase branch cables referred to as consumerservice cables, which during their installation are connected to thedistribution cable at service joint boxes.

' It is an object of the invention to provide a distribution cable ofthis kind which can be used without service joint boxes.

The distribution cable in accordance with the invention has branchcables permanently connected to it at spaced locations along its lengthbefore it is installed, each of which branch cables comprises at leastone insulated power conductor which is connected to a power conductorofthe distribution cable, and an outer concentric conductor which iselectrically and mechanically connected to the neutral conductor of thedistribution cable by a metal strip wrapped around the outer concentricconductor of the branch cable and the assembly of cores of thedistribution cable and permanently secured to the outer concentricconductor of the branch cable and to the neutral conductor of thedistribution cable.

Where, as is normal, the distribution and branch cables are eachprotected by a plastic sheath, each permanent connection between thedistribution cable and a branch cable at each spaced location along thelength of the distribution cable is preferably surrounded and protectedby a moulded body of plastic insulating material.

Some or all of the branch cables may be of sufficient length to be useddirectly as service cables or alternatively they may be in the form ofshort lengths to which service cables can be connected, for instance bythe method which is the subject of my British Pat. application 99 i hnatsntrhasb sramis under US. No. 1 185,598 and in which each of some orall of the branch cables has before the distribution cable is installed,permanently connected to its power and outer concentric conductors atits free end (that is the end not permanently connected to thedistribution cable) one part of an insulated two-part connector suitablefor connecting said power and outer concentric conductors to thecorresponding conductors of a consumer service cable.

The'invention also includes a method of permanently connecting a branchcable comprising at least one insulated power conductor and'a neutralconductor to a distribution cable of the kind specified before the distribution cable is installed, which method includes the steps of cuttingback an end of the branch cable to expose the neutral conductor and thepower conductor that is to be connected to a power conductor of thedistribution cable; applying a metal strip around the assembly of coresof the distribution cable and around the exposed neutral conductor ofthe branch cable; welding or otherwise permanently electrically andmechanically connecting the metal strip to the neutral conductor of thedistribution cable and to the neutral conductor of the branch cable;electricallyconnecting the exposed power conductor of the branch cableto a power conductor of the distribution cable; and applying insulationto the connections thus made, preferably by pouring or injecting aninsulating compound into a mould which is fitted around the distributioncable and which may or may not be removed after the insulating compoundhas set.

The invention is especially applicable to distribution cables in whichthe power conductors are individually insulated with rubber or plasticinsulation an in which the assembly of cores is protected by a rubber orplastic sheath and, when using the above described method of connectionfor such a cable, a part of the insulation of the power conductor of thedistribution cable is necessarily cut away to enable the power conductorof the branch cable to be welded or otherwise electrically connected andthe body of insulating material moulded around the connections can alsoreplace the part of the sheath necessarily cut away to gain access'tothe assembly of cores.

The distribution cable will normally be a three-phase cable and in thiscase the branch cable will generally, but not necessarily, be a singlephase cable comprising a single power conductor surrounded by an outerconcentric conductor. The metal strip for electrically and mechanicallyconnecting the neutral conductors of the distribution and branch cablesmay be preformed to a cross-sectional shape approximating that of adumbbell, one part of the dumb-bell having an internal diameterapproximating the external diameter of the outer concentric conductor ofthe branch cable and the other part of the dumb-bell being divided intotwo separable parts to facilitate application of the preformed stripover the assembly of cores of the distribution cable and being adaptedto have an internal diameter approximating the external diameter of theassembly of cores.

The assembly of cores of the distribution cable may be surrounded by anouter conductive layer in electrical contact with the neutral conductor,for instance a layer or layers of helically lapped metal tape. ln thiscase the metal strip is preferably welded or otherwise permanentlysecured both to the outer conductive layer and to the underlying neutralconductor by re moving a part of the outer conductive layer overlyingthe neutral conductor before the weld is effected. It will also benecessary to remove a part of the outer conductive layer overlying thepower conductor to which the power conductor of a branch cable is tobe-connected.

ltis convenient to connect two branch cables simultaneously to thedistribution cable at the same location and to use a single body ofinsulating material to surround and protect the connections made withboth branch cables;

Although the branch cables may each be permanently connected to thedistribution cable after the cables have been sheathed by removing partof the sheath of the distribution cable at each location where a branchcable is to be connected, the branch cables may alternatively bepermanently connected to the distribution cable before the cables aresheathed by arranging the branch cables each to extend alongside and bespaced from the distribution cable over substantially the whole lengthof the branch cables and by continuously extruding a sheathing body ofrubber or plastic material over the assembly so formed to embed thedistribution and branch cables therein.

The invention is further illustrated by a description, by way ofexample, of a four-core distribution cable in accordance with theinvention, with reference to the accompanying drawing which shows afragmental perspective view of the cable.

Referring to the drawing, the distribution cable 1 comprises three solidaluminium power conductors 2 each enclosed in an extruded insulatingcovering 3 of ethylene propylene rubber and a solid aluminium neutralconductor 4 enclosed in. an extruded lead covering 5, the cores soformed being helically laid up together and surrounded by an outerprotective sheath 6 of polyvinyl chloride. At each of a plurality oflocationsspaced along the length of the distribution cable 1 ends of twosingle-core branch cables 11 comprising a solid aluminium powerconductor 7, extruded insulation 8 of polyvinyl chloride, an outerconcentric stranded conductor 9, and a sheath 10 of polyvinyl chloride,which extend alongside the distribution cable, are permanently connectedto it.

In effecting the connections between the distribution and branch cablesa part of the sheath 6 is removed to expose the assembly of cores and,after cutting back the ends of the branch cables 11 in the normal way,the outer concentric conductor 9 of each branch cable is electricallyconnected to the neutral conductor 4 of the distribution cable byapplying a metal strip 12 about the conductor 9 and about the assemblyof cores and welding it to the conductor 9 and to the underlying neutralconductor 4. A part of the insulation 3 of the power conductor 2 towhich connection is to be made is removed, the conductors 7 of thebranch cables are welded to the exposed power conductor 2 and thecompleted joints are embedded in a moulded body 14 of polyvinyl chloridewhich bonds to the sheaths 6 and 10.

The method in accordance with the invention has the advantage that itsimplifies effecting of an electrical,

connection between the neutral conductors of the distribution and branchcables because the position of the power conductor of the distributioncable to which connection is to be made with respect to the neutralconductor is immaterial and the metal strip can be welded or otherwisepermanently electrically and mechanically connected to the neutralconductor at any point in its periphery that is in contact with theneutral conductor.

The distribution cable in accordance with the invention can bemanufactured and laid more economically then distribution cables atpresent in use since when installed it does not have to be opened up atspaced locations under restricted conditions in a cable trench for theconnections to a service cable to be made. These connections are mademuch more simply and satisfactorily, for example, in the factory or in aworkshop, before installation of the distribution cable and when thebranch cables are long enough to reach the consumers premises no outsidejointing on site is required. When short branch cables are provided theycan be connected during installation to lengths of service cable by asimple straight through joint or by a simple insulated two-partconnector.

What I claim as my invention is:

l. A distribution cable comprising a neutral conductor and a number ofinsulated power conductors all helically laid up together and havingbranch cables permanently connected to it at spaced locations along itslength before it is installed, each of which branch cables comprises atleast one insulated power conductor which is connected to a powerconductor of the distribution cable and an outer concentricconductorwhich is electrically and mechanically connected to the neutralconductor of the distribution cable by a metal strip wrapped around theouter concentric conductor of the branch cable and the assembly of coresof the distribution cable and permanently secured to the outerconcentric conductor of the branch cable and to the neutral conductor ofthe distribution cable.

2. A distribution cable as claimed in claim 1, wherein the metal stripis preformed to a cross-sectional shape approximating that of adumb-bell, one part of the dumb-bell fitting tightly around the outerconcentric conductor of the branch. cable and the other part of thedumb-bell being divided into two separable parts which together fittightly around the assembly of cores of the distribution cable.

3. A distribution cable as claimed in claim 1 wherein the assembly ofconductors of the distribution cable is surrounded by an outerconductive layer in electrical contact with the neutral conductor.

4. A distribution cable as claimed in claim 3, wherein the metal stripis permanently secured to the'outer conductive layer of the distributioncable.

5. A distribution cable as claimed in claim 1, wherein at least twobranch cables are connected at each of at least some of said spacedlocations along the length of the distribution cable.

' 6. A distribution cable as claimed in claim 1, wherein at least someof the permanently connected branch cables are of sufficient length tobe used directly as service cables.

7. A distribution cable as claimed in claim 1, wherein the powerconductors of the distribution cable and of the branch cables areindividually insulated with an insulating material selectedfrom thegroup of materials consisting of rubber and plastic materials andwherein the distribution cable and each branch cable are eachindividually protected by a sheath of an insulating material selectedfrom the group of materials consisting of rubber and plastic materials.

8. A distribution cable as claimed in claim 7, wherein each permanentconnection between the distribution cable and a branch cable at eachspaced locationalong gether, which method includes the steps of cuttingback.

an end of the branch cable to expose the neutral conductor and the powerconductor that is to be connected to a power conductor of thedistribution cable;

applying a metal strip around the assembly of cores of the distributioncable and around the exposed neutral conductor of the branch cable;permanently electrically and mechanically connecting the metal strip tothe neutral conductor of the fore the distribution cable is installed,said distribution cable comprising a neutral conductor and a number ofinsulated power conductors all helically laid up together, which methodincludes the steps of cutting back an end of the branch cable to exposethe neutral conductor and the power conductor that is to be connected toa power conductor of the distribution cable;

applying a metal strip around the assembly of cores of the distributioncable and around the exposed neutral conductor of the branch cable;permanently electrically and mechanically connecting the metal strip tothe neutral conductor of the distribution cable and to the neutralconductor of the branch cable; electrically connecting the exposed powerconductor of the branch cable to a power conductor of the distributioncable; fitting a mould around the distribution cable in the vicinity ofeach connection thus made; and introducing a hardenable insulatingcompound into the mould to insulate the connection. 11. A method asclaimed in claim 10, which includes the additional step of removing themold after the insulating compound has set.

1. A distribution cable comprising a neutral conductor and a number ofinsulated power conductors all helically laid up together and havingbranch cables permanently connected to it at spaced locations along itslength before it is installed, each of which branch cables comprises atleast one insulated power conductor which is connected to a powerconductor of the distribution cable and an outer concentric conductorwhich is electrically and mechanically connected to the neutralconductor of the distribution cable by a metal strip wrapped around theouter concentric conductor of the branch cable and the assembly of coresof the distribution cable and permanently secured to the outerconcentric conductor of the branch cable and to thE neutral conductor ofthe distribution cable.
 2. A distribution cable as claimed in claim 1,wherein the metal strip is preformed to a cross-sectional shapeapproximating that of a dumb-bell, one part of the dumb-bell fittingtightly around the outer concentric conductor of the branch cable andthe other part of the dumb-bell being divided into two separable partswhich together fit tightly around the assembly of cores of thedistribution cable.
 3. A distribution cable as claimed in claim 1wherein the assembly of conductors of the distribution cable issurrounded by an outer conductive layer in electrical contact with theneutral conductor.
 4. A distribution cable as claimed in claim 3,wherein the metal strip is permanently secured to the outer conductivelayer of the distribution cable.
 5. A distribution cable as claimed inclaim 1, wherein at least two branch cables are connected at each of atleast some of said spaced locations along the length of the distributioncable.
 6. A distribution cable as claimed in claim 1, wherein at leastsome of the permanently connected branch cables are of sufficient lengthto be used directly as service cables.
 7. A distribution cable asclaimed in claim 1, wherein the power conductors of the distributioncable and of the branch cables are individually insulated with aninsulating material selected from the group of materials consisting ofrubber and plastic materials and wherein the distribution cable and eachbranch cable are each individually protected by a sheath of aninsulating material selected from the group of materials consisting ofrubber and plastic materials.
 8. A distribution cable as claimed inclaim 7, wherein each permanent connection between the distributioncable and a branch cable at each spaced location along the length of thedistribution cable is surrounded and protected by a moulded body of aninsulating material selected from the group of materials consisting ofrubber and plastic materials.
 9. A method of permanently connecting abranch cable comprising at least one insulated power conductor and aneutral conductor to a distribution cable before the distribution cableis installed, said distribution cable comprising a neutral conductor anda number of insulated power conductors all helically laid up together,which method includes the steps of cutting back an end of the branchcable to expose the neutral conductor and the power conductor that is tobe connected to a power conductor of the distribution cable; applying ametal strip around the assembly of cores of the distribution cable andaround the exposed neutral conductor of the branch cable; permanentlyelectrically and mechanically connecting the metal strip to the neutralconductor of the distribution cable and to the neutral conductor of thebranch cable; electrically connecting the exposed power conductor of thebranch cable to a power conductor of the distribution cable; andapplying insulation to the connections thus made.
 10. A method ofpermanently connecting a branch cable comprising at least one insulatedpower conductor and a neutral conductor to a distribution cable beforethe distribution cable is installed, said distribution cable comprisinga neutral conductor and a number of insulated power conductors allhelically laid up together, which method includes the steps of cuttingback an end of the branch cable to expose the neutral conductor and thepower conductor that is to be connected to a power conductor of thedistribution cable; applying a metal strip around the assembly of coresof the distribution cable and around the exposed neutral conductor ofthe branch cable; permanently electrically and mechanically connectingthe metal strip to the neutral conductor of the distribution cable andto the neutral conductor of the branch cable; electrically connectingthe exposed power conductor of the branch cable to a power conductor ofthe distribution cable; fitting a mould arouNd the distribution cable inthe vicinity of each connection thus made; and introducing a hardenableinsulating compound into the mould to insulate the connection.
 11. Amethod as claimed in claim 10, which includes the additional step ofremoving the mold after the insulating compound has set.